Qestion about old evinrude V4

[jaredcando]

I have a 1979 Evinrude V4 100 horse. It runs fine for 15 mins then starts to run rough. It will idle real low untill it almost stalls then rev back up real quick to about 1300 rpms then start to slowly die back down again untill it almost stalls. this process just repeats. I think it has somthing to do with the engine getting hot. it is still peeing and the water coming out is warm but not hot. Also there is two holes under the Engine cowl on the top of the lower unit the i suspect to be exahust but some water is coming out of it also is this correct or do i have a leak somewhere. Also New Plugs and Filters and carb is clean. what could be the problem. thanks.

 

[jonesg]

Re: Qestion about old evinrude V4

I would suspect an air leak in the fuel plumbing, check the head temp with a cheap infra red thermometer (home depot).
Have you tried pumping the fuel bulb ?
what about hitting the choke?
Compression ok?

 

[jaredcando]

Re: Qestion about old evinrude V4

the bulb is a little loose i can tell but i can tell it still has fuel maybe 60% tightness on the bulb i can pump it up a little tighter but it makes no difference to the engine. the Choke is working fine kills the engie in abour 2 secs manual and electric. Compression test hasnt been done yet but i wouldnt think thats the problem cause i will run 40mph for 15 mins at 5200rpms before it starts acting up, but i am new to boats this is my first.

 

[Ozdog]

Re: Qestion about old evinrude V4

Sounds like a fuel delivery problem.

 

[jaredcando]

Re: Qestion about old evinrude V4

I hope so i would still like some more info on this if anyone has any ideas. If its a fuel problem i have eliminiated everything except new hoses and rebuild fuel pump. Pump has new O-rings and has been cleans so i dont think its that either. Its getting frustration not knowing what could cause this. i was told it could be a number of ignition parts that fail when they get warm.

 

[jaredcando]

Re: Qestion about old evinrude V4

I am hopping the replying to this will bring it back up to the top of the list so people will see it. i could really use some help trying to figure out what is wrong any help will be appricated. thanks

 

[jonesg]

Re: Qestion about old evinrude V4

You need to get a $10 spark gap tester from the auto store and test the spark with the gap set to 3/8th inch.
Warm the engine up before testing.
Should be a briught blue spark, not yellow.

 

[Solittle]

Re: Qestion about old evinrude V4

When was the last time you replaced the water pump and t-stats?

 

[jaredcando]

Re: Qestion about old evinrude V4

I just bought the boat last year i have not replaced the water pump since i have had it. The plugs are new and the correct ones but i will check the gaps on them this week. If the gaps are good what would be the next step to eliminate.

 

[emdsapmgr]

Re: Qestion about old evinrude V4

You have already done the easy test for fuel delivery: When the engine starts to slow down, constantly prime the bulb on the fuel hose. This will force extra fuel into the carbs. If the engine runs fine (incl. high speed) when constantly priming the fuel hose bulb, it could be a weak fuel pump. If you run off a built-in tank, don't forget to check the anti-siphon valve for debris inside. Since you have already tried that, checking for spark is the next thing. Possible you are losing spark-perhaps even one of the two power packs is bad once the engine warms up. It's easy to check all 4 plug wires with an inductive timing light when the engine is under load. It is normal for some water to exit the two exhaust relief holes at the top of the midsection. That water flow should increase dramatically when the boat is on plane.

 

[jaredcando]

Re: Qestion about old evinrude V4

thank you emdsapmgr. I was worried about the water in the exhaust i though the exhause was all under water but thank you i have an inline spark tester i will try that later this week and will let everyone know what i find.

 

[jaredcando]

Re: Qestion about old evinrude V4

ok everyone. i worked on her this weekend i did a spark plug test and found that one of the cylinders isnt getting much of a spark. I changed out the plug and same thing so i switched the coils around and still same problem on the same cylinder. what else could cause one cylinder to get very little spark. i did a comprssion test all cylinders between 120 and 124 so compression is great for her age. What else could be the problem to only affect one cylinder when it gets warmed up.

 

[emdsapmgr]

Re: Qestion about old evinrude V4

Weak ignition components tend to break down when the engine heats up to normal operating temps. That's smart thinking to swap the coils. You found out the problem still exists on that same cyl. You can further test- by swapping the two power packs. If the problem moves to the other head when you swap the packs, likely one of the two power packs is bad. That's excellent compression.

 

[jaredcando]

Re: Qestion about old evinrude V4

Thanks that will be my next step to try. I will get on that as soon as i can. I will keep everyone posted with my results.

 

[dhachtel]

Re: Qestion about old evinrude V4

jaredcando.... We are having the same problems. I have a 78 Evinrude 115hp. I can leave the dock and plane out and run about 60 seconds or so and then mine just cuts out. So I replaced both power packs and that didn't help. My fuel bulb collapses even with the vent completely open. The next thing I am going to try is rebuilding the fuel pump. Mine just seems to cut in and out. I'm lost on whether it's fuel or ignition still. Let me know how your turns out. We could have the same problem. I'll do the same. Thanks

 

[jonesg]

Re: Qestion about old evinrude V4

Uh you already have your answer, its not the same problem , just similar symptoms.

 

[jaredcando]

Re: Qestion about old evinrude V4

dhachtel it seems your problem is similar but not the same my fuel bulb stays pretty tight and my boat will run for 20 mins at 5000rpms before it starts acting up and it still runs just really rough and speratic. i just dont want you to be using this as a guide to fix your boat when it might not be the same problem as mine.

 

[boobie]

Re: Qestion about old evinrude V4

dhachtel, you may want to start your own thread as you'll probably get a better response and not confuse issues.

 

[jaredcando]

Re: Qestion about old evinrude V4

Sorry everyone i have been on vacation and havent had time to work my boat, but i finaly switched the powerpacks around and instantly noticed that the engine had much stronger sparks all the way around. I dont know why but i could not get the motor to act up after beeing on muffs for almost thirty mins, at all ranges of rpms. I still dont think i have solved the problem all i did was move the powerpacks to opposite sides but i will take it out as soon as the water level drops here in MS, water is so high cant get to boat ramps.